A steel making electric arc furnace (which may be referred to as “electric furnace”) employs an intermittent running operation performed by use of cycles, each of which includes steps as follows. At first, a source material, such as iron scrap, reduced iron (DRI), hot briquette iron (HBI) prepared by processing the DRI at a high temperature, molten iron, or cold iron (ingot iron), is charged into the furnace. Then, an electrode is inserted into the electric arc furnace and an electric power is applied to the electrode to melt the source material. Then, the electric power is stopped, and the molten steel is tapped out.
Iron scrap used as the source material is sometimes accompanied with paint and/or machine oil applied thereto, and so white smoke and/or evil smell may be generated due to unmixed synthetic resins. Further, carbon monoxide is generated due to carbon contained in iron scrap and/or DRI. In light of this, air is forcibly taken into the space between the furnace and furnace lid and/or into the secondary combustion chamber to achieve complete combustion of the exhaust gas.
Since this combustion gas has a high temperature higher than 1,200° C. and thus has a large amount of energy, attempts have been made to recovery its waste heat. For example, Patent Document 1 discloses a technique for recovering the sensible heat and/or combustion heat of exhaust gas discharged from a steel making electric arc furnace, by use of a waste heat boiler disposed in the exhaust gas pipe line of the electric furnace.
Further, recovered steam can be used for electric power generation by a steam turbine or the like. When the steam is supplied as a driving source for the steam turbine, the steam is preferably formed of superheated steam to increase the enthalpy at the inlet port of the turbine. In light of this, Patent Document 2 discloses a technique that recovers waste heat from a steel making electric arc furnace as saturated steam and then turns the steam into superheated steam.